Whisk the water, fish sauce substitute, brown sugar, lime zest, lime juice, cornstarch, and red pepper flakes in a small bowl until the sugar and cornstarch are completely dissolved.

Heat a small portion of the oil in a 12-inch nonstick skillet over medium-high heat until the oil shimmers but does not smoke. Add the garlic and ginger and cook, stirring constantly, until fragrant and just beginning to color. Transfer the aromatics to a small bowl.

Wipe out the skillet and heat the remaining oil over medium-high heat. Add the eggplant and bell pepper and cook, stirring occasionally, until the eggplant is deeply browned on the edges and tender, about 10 minutes.

Return the garlic mixture to the skillet. Give the sauce a quick whisk to lift any cornstarch that has settled at the bottom, then pour it over the vegetables.

Simmer the mixture until the sauce thickens into a glossy glaze that coats the vegetables, about 1 minute.

Remove the skillet from the heat and stir in the basil and scallions. Serve hot with steamed rice.